SIMBAD references

The metal-rich bulge globular clusters NGC6388 and NGC6441 show distinct blue horizontal-branch tails in their color-magnitude diagrams. They are thus strong cases of the well known Second Parameter Problem. In addition, the horizontal branches in these globular clusters show an upward tilt toward bluer colors, which cannot be explained by canonical evolutionary models. We will discuss several scenarios which have been proposed to explain these two features and present observations obtained to test these scenarios.